There is a conventional packet transfer system in which a terminal unit sends in a preparatory communication stage test packets in a trial class whose priority is lower than an originally intended priority, and according to a result thereof, determines whether or not communication is possible and communication quality is securable. This is called a terminal-initiative, measurement-based call admission control system. (For example, Viktoria Elek, Gunnar Karlsson, and Rovert Ronngren, “Admission control based on end-to-end measurements,” Infocom 2000, U.S.A., IEEE, Mar. 29, 2000.)
Such terminal-initiative, measurement-based admission control employs a band securing communication method that provides a terminal with functions of state management and admission control for each communication (“communication” being synonymous with “flow” in this specification), to reduce processing load on a communication network, realize scalability, and save communication costs.
In such a system, test packets in a trial class are sent, and if a result thereof is failure, are again sent. In this case, each terminal in the system freely tries to resend packets without regard to a load condition at the moment. This produces an overflow of trial packets in an overload state and decreases a total throughput.
To cope with the total throughput decrease due to an increase in the quantity of packets to be communicated, no techniques have been proposed that can change a frequency of retry attempts according to a total throughput or synchronize retry timing with a total throughput to avoid useless collisions.
According to the terminal-initiative, measurement-based admission control, a packet transfer apparatus such as a router in a packet network employs priority control queues of Diffserv (differentiated services) type.
A typical example will be explained. A priority class is to transfer an original flow and a trial class is to transfer test packets. An upper limit is set on a total band of the priority and trial classes. The priority class is transferred preceding to the trial class. An assumption is made that a 100-Mbps transmission line has an upper limit total band of 40 Mbps and a flow of 35 Mbps of the priority class is already present in the transmission line. If there is a request for a new flow and if the requested flow is 5 Mbps or smaller, test packets for the request are transferable in the trial class. If a receiver terminal of the test packets notifies the sender terminal of acceptance, the sender terminal sets a new flow in the priority class. If the requested new flow is of over 5 Mbps, the test packets deteriorate during transmission and the sender terminal receives a faulty result from the receiver terminal. Then, the sender terminal does not start an originally intended transmission flow.
According to this architecture, a router restricts flow rates class by class without conducting flow-by-flow state management or admission determination. Only thereby, a communication system including terminals can achieve admission determination and guarantees the qualities of individual flows.
A typical example of architecture for monitoring and restricting flow rates is UPC of ATM. The UPC stipulates an ATM capacity to monitor a total band involving priority-class cells of CLP=0 and trial-class cells of CLP=1. When a violation occurs, this architecture simply discards even priority-class cells or changes priority-class cells into non-priority-class cells.
It is preferable, however, that a priority-class flow, once admitted, is continuously transferred as it is without being discarded, irrespective of a total band upper limit. There will be a particular case to immediately admit a flow in the priority class without regard to a total band upper limit or without conducting a test process in the trial class. Such a particular case will be explained in three examples.
A first example is a band variation in a variable band flow. Communication with variable flow rates causes a situation in which an actual communication band drops below a test packet communication band. For example, there is a transmission line with an upper limit of 40 Mbps, and the transmission line is presently transmitting ten 4-Mbps flows. If each flow drops to 3.5 Mbps, an actually used band total will be 35 Mbps to provide a margin of 5 Mbps. At this time, to establish a new flow of 5 Mbps, trial-class test packets are sent at 5 Mbps. Due to the margin in the band at this moment, a receiver terminal confirms a good quality, and therefore, a new priority-class flow is actually set. If the existing flows return each to the original communication band of 4 Mbps thereafter, the total band will be 45 Mbps. Then, an excess of 5 Mbps over the upper limit of 40 Mbps is discarded according to the related art. This affects all of the flows, to drastically decrease the throughput of a communication network as a whole. To avoid this, there is a technique of sending test packets in a band larger than an originally intended band. Namely, in the above example, test packets are sent at 6 Mbps that is greater than the originally intended flow rate of 5 Mbps, to avoid the problem. This technique of stabilizing the traffic of a whole network, however, greatly increases the number of test packets in each flow. In addition, the technique frequently fails to establish new flows, in particular, in access sections involving narrow bands. This technique, therefore, is inefficient. There is another technique that absorbs traffic variations by extending a measurement period of test packets. This, however, extends a time to determine the possibility of establishing a flow, and therefore, deteriorates serviceability.
It is desirable to continuously transfer a once-accepted priority-class flow at 5 Mbps without regard to flow-rate variations.
Second and third examples mentioned below relate to immediately admitting a priority-class flow without a trial-class test procedure or without regard to an upper limit total band.
The second example relates to a circuit that is forcibly switched to another. There is a system that employs a spare communication circuit for a circuit failure. In FIG. 18, two circuits are prepared between two packet transfer apparatuses 11h and 11i. It is supposed that load is distributed flow by flow to the circuits according to a certain method. If one (for example, the circuit A) of the circuits fails, a flow X that is unable to be transferred through the circuit A is entirely transferred to a spare circuit (for example, the circuit B). If the spare circuit (circuit B) has a flow Y before the failure, the sum of the flows exceeds the capacity of a single circuit, and therefore, discarding will occur without regard to the flows X and Y. In this example, it is assumed that each circuit has an upper limit of 40 Mbps and is transferring priority-class packets at 35 Mbps. If one of the circuits fails in this state, the priority-class packets are tried to be transferred at 70 Mbps through the normal circuit. Then, packets for 30 Mbps exceeding the upper limit of 40 Mbps are discarded. In this case, discarding a specific flow is impossible to carry out unless information on each flow is stored in routers. Accordingly, all of the flows are affected thereby to drastically decrease the throughput of a communication network as a whole.
In such a case, it is desirable to continuously transfer at least priority-class flows even if the capacity of a circuit is exceeded after switching a failed circuit to another. In this case, a priority-class flow in the failed circuit must continuously be transferred as it is in the new circuit without a test procedure using trial-class packets.
The third example relates to the handover of a mobile terminal. When carrying out the handover of a mobile terminal, the above-mentioned related art sends test packets to a new communication path serving as a handover target path and determines whether or not communication is possible. If the new communication path is in use by priority-class packets up to the upper limit thereof and if a new flow is handed over to the communication path, the handed-over flow will have an insufficient communication quality. In addition, like the two examples mentioned above, the communication qualities of the existing flows in the communication path are also badly affected.
It is desirable to immediately continue the handed-over flow in the priority class in the new communication path irrespective of the upper limit of the path.
Also, the terminal-initiative, measurement-based call admission control system of the related art mentioned above has problems mentioned below.
Namely, when the related art provides a public communication service in which a terminal can determine communication possibility in a perfectly autonomous and distributed manner by transferring test packets whose priority is lower than priority packets used in normal communication, there are some conditions. To control an actual flow rate, a call control apparatus must conduct primary admission determination including confirmation of service subscription, and an edge packet transfer apparatus must monitor the quantities of packets sent by users. In addition, the edge packet transfer apparatus must monitor a priority transition. The call control apparatus must always control the edge packet transfer apparatus, so that the edge packet transfer apparatus correctly performs the monitoring task. For this, the call control apparatus must frequently exchange control signals with the edge packet transfer apparatus. This results in increasing a necessary communication band and process load.
Packet rate monitoring by a conventional quality guaranteeing packet transfer system measures only a maximum flow rate. According to the terminal-initiative, measurement-based admission control, a reduction in communication amount or a communication suspension by a terminal is regarded as a communication availability in a communication network. Accordingly, a test packet sent from another terminal at this time is admitted as new communication.
Requirements for the conventional terminal-initiative, measurement-based call admission control system mentioned above will be explained.
The terminal-initiative, measurement-based call admission control system disclosed in the above-mentioned document has characteristics mentioned below, and therefore, requires the precise monitoring of terminal operation. Namely, a transmission side must send test packets to confirm a communication quality before establishing communication, and a reception side must correctly inform the transmission side of a packet receiving state. According to the packet receiving state, the transmission side must determine whether or not it is possible to send regular communication packets. The regular communication packets must be sent in a band that is narrower than that for the test packets but not too narrow. These conditions are essential for proper terminal operation. This communication system, therefore, must more precisely monitor terminal operation than a conventional network-initiative call admission control system. Whether or not the system properly functions with these conditions influences the operating cost of the system. The conventional terminal-initiative, measurement-based call admission control system, however, lacks the detailed examination of terminal monitoring.
When monitoring terminal operation by a monitor apparatus in a network according to the terminal-initiative, measurement-based call admission control system mentioned above, the monitor apparatus is unable to know a quality deterioration occurring in a section between the monitor apparatus and a receiver terminal. Even if a quality in the section is insufficient, the reception side can intentionally notify that the quality is good. Such a fraudulent operation must be detected.
The conventional terminal-initiative, measurement-based call admission control system sends in a preparatory communication stage test packets in a trial class whose priority is lower than an originally intended priority, and according to a result of the trial communication, sends packets in a priority class that is of the originally intended priority or again in the trial class. With this configuration, the system is unable to clarify the timing to charge a terminal apparatus for a fee.
The present invention has been made in consideration of one of the above-mentioned situations. An object of the present invention is to monitor packet traffic and the quality thereof and control packet transmission according to a result of the monitoring. For example, according to the monitoring result, control is made to send priority-class packets, or to retry trial-class packets, or to immediately stop trial-class packets, or to carry out synchronous transmission based on a probability, thereby preventing a traffic jam at terminals and improving a total throughput.
The present invention has been made in consideration of another of the above-mentioned situations. An object of the present invention is to cope with a packet that must immediately be admitted as a priority-class packet irrespective of a flow-rate limit and guarantee the quality of an admitted flow until the end of the flow.
The present invention has been made in consideration of still another of the above-mentioned situations. An object of the present invention is to carry out terminal-initiative, measurement-based admission control involving the transfer of test and priority packets at their respective priority levels without increasing process load while properly monitoring the type of service (ToS) of each packet and a flow rate of packets at low cost.
The present invention has been made in consideration of still another of the above-mentioned situations. An object of the present invention is to provide a monitor apparatus for monitoring terminal operation so that packets related to communication to be monitored are transferred through the monitor apparatus. This realizes centralized monitoring to reduce the facility cost of a packet transfer apparatus and the operation cost of a packet transfer system.
Another object of the present invention is to provide a monitor apparatus capable of separately monitoring a phase of determining admission possibility based on test packets and a phase of conducting proper communication, thereby expanding the number of communication sessions to be monitored and reducing the cost of the monitor apparatus per communication session.
Still another object of the present invention is to intentionally discard, by a monitor apparatus, test packets sent from a sender terminal, to monitor whether or not a receiver terminal correctly notifies the sender terminal of a reception result.